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  1. U

    A question about basic audio processing

    For the record, for 11 meter rigs, a balanced modulator is only used for SSB modes. The Cobra 148GTL in particular uses a different modulation scheme for AM. (Several ham radios do use a balanced modulator for both SSB and AM, but not CB or export rigs.) Improving audio response boils down to...
  2. U

    D104's anyone???

    (Sorry for being late to the party, I know this thread's a little old. :) ) If those mics were kept in a storage locker, there's a good chance the D104s are all ruined. The D104 crystal elements are vulnerable to extreme heat and humidity; prolonged exposure can damage them. And I doubt the...
  3. U

    Some nice DX on 20 meters last night

    I have a big problem with QRN at my place -- too much man-made noise living in a big city like San Francisco -- but sometimes you get a nice surprise. Last night I managed to work RI1ANT at Mirny Base in Antarctica on 20 meters (14.209). I did it on my home-brew 88' doublet too with just 150...
  4. U

    Greetings

    Oh, I think I remember now. We talked on 38LSB, but it was rough due to all the skip. Glad you got through to Bob 941 too. I'm sometimes on channel 17 in the evenings. I work in Alameduh. Gotta love the reverse commute. -Bill, Unit248
  5. U

    Greetings

    Hey, 222, whereabouts are you in San Francisco? I'm in the Civic Center area (couple blocks from city hall). There's a chance we've talked before but I can't place your number offhand. -Bill, Unit 248
  6. U

    Just worked northern Italy on 27USB!

    Sometimes you're in the mud even with a ticket. I heard a Kuwait station on 20 meters last night (9K2UU) and tried for about half an hour to get a call through to him, but I'm only running 150 watts and a wire antenna. All the big strappers walked all over me until he went QRT. :( Not much I...
  7. U

    carrier or modulation

    KM3F is right on the money. This can get a little messy once you factor in an amplifier though. The problem is that you need to determine your amplifier's peak output power level and then divide that by 4 in order to decide how much AM carrier power to use. What makes that hard is that most...
  8. U

    New radio on a budget

    HF rigs usually have multiple output filters (low pass) for different bands. Sometimes they're switched with relays, other times with PIN diodes. If 40-160 is shot, but you still get full output on 20 through 10 meters, you may have a bad relay or blown diode that's causing the wrong filter (or...
  9. U

    HIFI audio on AM, ts-430s?

    The TS-850 has configuration menu that lets you adjust certain functions. It isn't very sophisticated, but it's there. For example, normally the radio emits a set of morse code beeps through the speaker when you select a mode, to announce what mode you just chose (AM, FM, USB, LSB, CW). The...
  10. U

    Technician's first radio

    If you're looking for an HF radio, a lot of the older Kenwood rigs go for around $300 to $400, including the TS-430S, TS-440S and TS-140S. The 440 is the only one that has a built-in antenna tuner though, and it's a bit more to the high end of the scale (around $450). Another possible option...
  11. U

    HIFI audio on AM, ts-430s?

    I would investigate some of the HiFi AM mods for the TS-440. The 440 and 430 both use the same AM transmission scheme (unbalancing the AN612 balanced modulator). As has been noted, the key issue is filtering: direct injecting the balanced modulator will help you avoid any limitations in the mic...
  12. U

    ic718 swings backwards

    Ask your friend how much ALC indication he's seeing when he talks. (Press the meter function select button until it displays ALC.) The manual recommends setting the radio so that the ALC indication remains within the ALC zone (which will be indicated on the display). This is typically ok for...
  13. U

    Choice of transceivers

    Hm. I have a TS-850SAT and I've never had issues with the FM squelch on it. I do have problems with the squelch on the TS-950SDX though. The rig isn't broken, but the design of the squelch circuit makes it a bit too sensitive for people like me that live in big cities with lots of man-made radio...
  14. U

    Kenwood 990 Coming Next Month

    The TS-950SDX also uses power MOSFETs: Motorola MRF150s, also run at 50 volts (well, 48 volts, but close enough). That radio is designed for 150 watts rather than 200, but the VRF150 is a heavier duty part. According to Kenwood's literature, it was the first HF amateur rig to use FETs intead of...
  15. U

    Galaxy 2547 Freq Response Question

    I was under the impression that the Cobra 148 didn't use the balanced modulator for AM transmit modulation (only for SSB). Am I wrong? Confused? Misinformed? (I know some ham rigs generate AM that way, but I thought for CBs it was different.) Also, I have a question for The Bruce: how are...
  16. U

    Cobra 2000 gtl NO Modulation

    Yeah, the MC-320 crystal element in the head would not react well to being stored at those temperatures. As a last resort, you can try double-checking if the contacts in the neck just need cleaning (after 12 years they may have oxidized a bit) but chances are good the element is shot. If you...
  17. U

    Cobra 2000 gtl NO Modulation

    There's no second battery in the mic head, but the D104 mic element is made using a Rochelle salt crystal. The crystal can be damaged by extreme temperature changes, humidity or physical shock. Humidity is a problem because moisture can dissolve the crystal (just like regular salt)...
  18. U

    Cobra 2000 gtl NO Modulation

    I hate to say it, but based on what others have said, I think your best bet is just to replace all the electrolytic capacitors in one go. You might be able to run down the one cap that's causing you trouble now, but you'll just have another one go bad later. It'll turn into a long, drawn-out...
  19. U

    Carrier VS. Swing on AM...

    This is an unmodulated carrier: This is actually a sine wave, but it's oscillating at such a high frequency that on this oscilloscope display, all the lines bleed together and look like a single bar. (If you have a decent oscilloscope, you can crank up the timebase knob until it looks like a...
  20. U

    Kenwood TS-850S or Icom IC-756 non pro????

    While I'm a Kenwood fan and the TS-850S/AT is a nice radio (I own one), if I had to choose between the TS-850/SAT and the Icom IC-756, I'd grudgingly have to go with the Icom. The simple fact is the IC-756 has more features: - HF and 6 meters (TS-850 is HF only) - Built-in digital...